The present invention relates to an improvement on pistons for internal combustion engines which are susceptible to the undesirable build-up of carbon deposits, particularly on the walls and bottom of the compression ring grooves.
The build-up of carbon deposits on these portions of the compression ring grooves is very common owing mainly to the incomplete fuel burn at the upper region of the cylinder liner and/or to the carbonization of lubricating oil caused by high combustion temperatures.
The carbon that builds up on said areas is a complex composition which sticks at first to the piston on its top portion, or to the cylinder liner, then passes to the piston ring band and enters the compression ring grooves through the clearances between the groove walls and the faces of the rings. Tiny carbon particles adhere gradually to the bottom of the ring grooves and are subsequently densified by piston pounding force applied to the carbon by the rear face of the compression rings resulting from the piston secondary lateral motions.
This is a highly undesirable process, for the carbon deposit, as it increases substantially, urges the compression rings towards the cylinder wall, causing the shearing of the lubricating oil film between the cylinder and the ring front face. Thus, the resulting friction generates an abrasive action between said surfaces causing damages to the engine.
Only a few solutions for overcoming this problem have been proposed to this date. One well-known solution contemplates the mounting of the compression rings in a slant position in relation to the compression ring groove walls, the front face of these rings closer to the piston upper portion. This configuration prevents carbon from building up in the grooves as it eliminates the clearance between the compression ring upper face and the groove upper wall through which the carbon residues usually enter. However, this design causes an increase in lubricating oil consumption.